The present invention relates to an accumulator type fuel injection system for controlling the injection of fuel with use of an accumulator type unit injector.
Generally, an accumulator type fuel injection control system is mounted in a fuel supply system of a diesel engine, and provided with an accumulator type unit injector in the fuel supply system, a fuel pressure pump, and a controller which functions as a control system.
In the accumulator type fuel injection control system for a diesel engine, therefore, a plunger is driven by an eccentric cam, which is driven in interlock with a crank shaft of the engine, and a fuel of a low pressure, which has been fed into a pump chamber by means of a feed pump, is pressurized to a high pressure and then fed to an accumulator. In accordance with an operating condition of the engine, a drive command is outputted from the controller to an electromagnetic actuator to open or close a spill valve, whereby the fuel pressure in the accumulator is controlled to a high level. On the other hand, a signal indicating the fuel pressure in the accumulator is fed back to the controller from a fuel pressure sensor.
The high-pressure fuel present in the accumulator is fed to a fuel reservoir through a feed hole of a fuel injection nozzle to urge a needle valve in its opening direction. When the fuel injection nozzle is not in operation, an electromagnetic actuator of a three-way solenoid valve is de-energized and the high-pressure fuel in the accumulator is fed to an oil chamber. A hydraulic piston applies a depressing force based on such hydraulic pressure to the needle valve, whereby the needle valve is held in its closed position.
When the electromagnetic actuator is energized in accordance with a drive command outputted from the controller, the oil chamber is connected to a fuel tank by means of the three-way solenoid valve and the fuel pressure exerted on the hydraulic piston is relieved, so that the needle valve is opened by virtue of a pressure spring, and the high-pressure fuel present in the fuel reservoir is injected into a cylinder through the nozzle hole.
In such an accumulator type fuel injection control system for a diesel engine, the amount of fuel to be injected is calculated and set in the controller on the basis of both engine speed and accelerator opening. Fuel injection pressure and fuel injection timing are determined on the basis of both engine speed and fuel injection volume. Therefore, the control system controls the electromagnetic actuator on the basis of both fuel injection pressure and fuel injection volume so that a required amount of fuel is injected at a required pressure.
For example, such an accumulator type fuel injection control system is disclosed in Japanese Patent Laid Open No.93936/94.
In the accumulator type fuel injection control system for a diesel engine as described above, the fuel tank is provided on the vehicle body side, while the fuel pressure pump and the injection nozzle, with fuel supplied thereto from the fuel tank, are provided on the engine side. Since the engine vibrates during operation, it is supported to limit rolling motion with respect to the vehicle body by means of a mount. Therefore, a hose on the engine side extending from the injection nozzle is connected to a pipe on the vehicle body side through a rubber hose, and this piping is extended up to the fuel tank. On the other hand, a pipe on the engine side extended from the fuel pressure pump through the feed pump is also connected to a pipe on the vehicle body side through a rubber hose, and this piping is extended up to the fuel tank.
In the injection nozzle, the electromagnetic actuator is energized in accordance with a drive command outputted from the controller, and by an operation of the three-way solenoid valve, the fuel in the oil chamber is discharged to the fuel tank through a pipe and a rubber hose or the like. The amount of fuel thus discharged into the fuel tank is almost equal to or larger than the amount of fuel injected and it is an amount of return. This fuel is in a condition of high temperature due to the heat generated when the fuel is pressurized by the fuel pressure pump after the high-pressure injection of fuel has been continued for a long time or due to the heat generated as a result of conversion from energy generated when the pressurized fuel is released to the atmospheric pressure through the injection nozzle which injects the fuel at a high pressure.
Consequently, a large amount of fuel held at a high temperature is discharged from the injection nozzle into the fuel tank through the pipe and rubber hose. There has so far been the likelihood of the rubber hose being damaged when the high-temperature fuel flows in a large amount through the rubber hose. There has also been the problem that the deterioration of the fuel tank which is made of resin and which holds the return fuel of high temperature therein, is accelerated.
The present invention solves the above-mentioned problems. It is an object of the invention to provide an accumulator type fuel injection control system and the method thereof wherein the temperature rise of fuel flowing to a fuel return system is suppressed to prevent damage of the members used in the fuel return system and improve the safety.